Venus’ Winds Are Mysteriously Speeding Up

High-altitude winds on neighboring Venus have long been known to be quite speedy, whipping sulfuric-acid-laden clouds around the superheated planet at speeds well over 300 km/h (180 mph). And after over six years collecting data from orbit, ESA’s Venus Express has found that the winds there are steadily getting faster… and scientists really don’t know why.

By tracking the movements of distinct features in Venus’ cloud tops at an altitude of 70 km (43 miles) over a period of six years — which is 10 of Venus’ years — scientists have been able to monitor patterns in long-term global wind speeds.

What two separate studies have found is a rising trend in high-altitude wind speeds in a broad swath south of Venus’ equator, from around 300 km/h when Venus Express first entered orbit in 2006 to 400 km/h (250 mph) in 2012. That’s nearly double the wind speeds found in a category 4 hurricane here on Earth!

“This is an enormous increase in the already high wind speeds known in the atmosphere. Such a large variation has never before been observed on Venus, and we do not yet understand why this occurred,” said Igor Khatuntsev from the Space Research Institute in Moscow and lead author of a paper to be published in the journal Icarus.

Long-term studies based on tracking the motions of several hundred thousand cloud features, indicated here with arrows and ovals, reveal that the average wind speeds on Venus have increased from roughly 300 km/h to 400 km/h over the first six years of the mission. (Khatuntsev et al.)

A complementary Japanese-led study used a different tracking method to determine cloud motions, which arrived at similar results… as well as found other wind variations at lower altitudes in Venus’ southern hemisphere.

“Our analysis of cloud motions at low latitudes in the southern hemisphere showed that over the six years of study the velocity of the winds changed by up 70 km/h over a time scale of 255 Earth days – slightly longer than a year on Venus,” said Toru Kouyama from Japan’s Information Technology Research Institute. (Their results are to be published in the Journal of Geophysical Research.)

Both teams also identified daily wind speed variations on Venus, along with shifting wave patterns that suggest “upwelling motions in the morning at low latitudes and downwelling flow in the afternoon.” (via Cloud level winds from the Venus Express Monitoring Camera imaging, Khatuntsev et al.)

A day on Venus is longer than its year, as the planet takes 243 Earth days to complete a single rotation on its axis. Its atmosphere spins around it much more quickly than its surface rotates — a curious feature known as super-rotation.

“The atmospheric super-rotation of Venus is one of the great unexplained mysteries of the Solar System,” said ESA’s Venus Express Project Scientist Håkan Svedhem. “These results add more mystery to it, as Venus Express continues to surprise us with its ongoing observations of this dynamic, changing planet.”

So how cool is that? Am wondering after atmospheric temperature (profile) measurements. Have they increased? Or is it possible Venus is experiencing increased volcanic activity – thereby injecting volatiles into it’s atmosphere and causing it to expand? OR, could it be that as we approach solar maximum Venus’ atmosphere is heating up and thereby thinning out and speeding up? Maybe a combination of the above? Inquiring minds want to know!

Take another look… when the speed indicated by the white line is at 300km/hr, the black line is at the same value. When the white line is at 400km/hr the black line is approx. ~375km/hr. Thus the two lines seem to represent two data sets, not simply conversion factors. Could be that these soundings represent depth?

This quote is taken from the ESA Venus Express page which Jason has linked to above.
” In this graph, the white line shows the data derived from manual cloud tracking, and the black line is from digital tracking methods. “

A day on Venus is longer than its year, as the planet takes 243 Earth days to complete a single rotation on its axis.

Technically, this is not correct. Although Venus’ rotation period is longer than its orbital period, its solar day is actually 116.75 Earth days long; the Venusian year is about 1.92 Venusian days long.

The difference between the solar day v.s. the sidereal day is not because of the rotation of Venus, which is opposite to the other Planets, but it’s because of the slowness of Venus rotation, which allows the planet to travel further along is orbital path therefore the solar day needs to be further adjusted for the 24hr period

Hmmm…last six years, exactly during the rise of the current solar sunspot cycle. Venus is quite a bit closer, so the increased energy bombardment due to solar activity would be quite a bit higher there than on Earth. Even here, we have measured significant atmospheric disturbances due to the cycle. I’ll be quite interested in what happens as we pass the maximum and head towards lower solar activity.